Energy and exergy analysis of all-glass evacuated solar collector tubes with coaxial fluid conduit

In this research work, all-glass evacuated solar collector tubes with coaxial fluid conduit for T-type and H-type models with forced convection flow have been modeled. These models are based on an analytical solution of energy balance equations for various components of the collector's tube. On comparison, the results obtained in this work show good agreement with the results of previous research. The effects of changing the working fluid and the properties of the delivery tube and absorber tube on the working fluid temperature distribution in the collector tube have been investigated. Also the effect of the mass flow rate, solar radiation intensity, inlet temperature, ambient temperature, and optical efficiency and the length of collector tube on the outlet temperature of the fluid, energy efficiency and exergy efficiency in both models, have been studied. The results show that the changing delivery tube thermal conductivity and emission coefficients have no effect on the outlet temperature of the collector tube, but using selective coating absorber tube, increases collector tube outlet temperature for both models. The results also illustrate that in the H-type model the outlet flow temperature and exergy efficiency for both air and carbon dioxide as working fluid is greater than the T-type model.